The activation of neurotransmitter receptors at synapses mediate synaptic transmission upon being bound by neurotransmitters released from presynaptic terminals. The predominant inhibitory transmitter in the brain is gamma-aminobutyric acid (GABA), and ionotropic GABAA receptors localize at inhibitory synapses to mediate fast inhibitory transmission. Dysregulation of GABA receptors causes various mental and neurological disorders including autism spectrum disorder, schizophrenia, epilepsy, and other disorders. However, precise mechanisms for synaptic localization of GABAA receptors remain unclear. We have recently identified novel GARLH family proteins as a critical regulator of synaptic GABAARs. In this proposal, we aim to reveal in vivo roles of GARLHs in regulating GABAAR activity in the brain, principle rules of GARLH-GABAAR interactions, and molecular relationships of constituents of inhibitory synapses. Successful completion of this proposed work will reveal fundamental molecular mechanisms for determining synaptic localization and transmission of GABAA receptors in the brain. Elucidating the molecular rules governing inhibitory transmission will enable us to identify putative molecular targets for drugs that may alleviate impair neurological and mental disorders.